FIG. 1 shows an embodiment of a non-roaming architecture for Third Generation Partnership Project (3GPP) accesses. A UE 101 is served by a Radio Access Network (RAN) node (not shown). The RAN node may be a base station such as a NodeB, an evolved NodeB (eNB, eNodeB), or any other network unit capable of communicating over a radio carrier with the UE 101. The RAN node is comprised in a RAN such as E-UTRAN 103 as illustrated in FIG. 1. E-UTRAN is short for Evolved-UMTS Terrestrial Radio Access Network and UMTS is short for Universal Mobile Telecommunications System. LTE-Uu is the radio protocol of E-UTRAN between the UE 101 and the eNodeB of the E-UTRAN 103. LTE is short for Long Term Evolution.
An MME 105 comprises functions such as Non Access Stratum (NAS) signaling, NAS signaling security, inter Core Network (CN) node signaling for mobility between 3GPP access networks etc. S1-MME is the reference point for the control plane protocol between E-UTRAN 103 and the MME 105.
FIG. 1 shows two gateways, the Serving GateWay (SGW) 108 and the Packet data network GateWay (PGW) 110. The SGW 108 is the gateway which terminates the interface towards E-UTRAN 103. S1-U is the reference point between E-UTRAN 103 and the SGW 108 for the per bearer user plane tunneling and inter eNodeB path switching during handover. The PGW 110 is the gateway which terminates the SGi interface towards the Packet Data Network (PDN). The PDN in FIG. 1 is represented by the Operator's IP Services (e.g. IMS, PSS etc.) 113. S5 is an interface which provides user plane tunneling and tunnel management between the SGW 108 and the PGW 110. IMS is short for Internet protocol Multimedia Subsystem and PSS is short for Packet Switched Streaming.
The Serving GPRS Support Node (SGSN) 115 keeps track of the location of the UE 101 and performs security functions and access control. The SGSN 115 is connected to the GERAN 118 and/or to the UTRAN 120. GPRS is short for General Packet Radio Service. GERAN is short for GSM EDGE Radio Access Network, where GSM is short for Global System for Mobile Communications and EDGE is short for Enhanced Data for Global Evolution. UTRAN is short for UMTS Terrestrial Radio Access Network. S3 is the reference point between the MME 105 and the SGSN 115 and enables user and bearer information exchange for inter 3GPP access network mobility in idle and/or active state. S4 is a reference point which provides related control and mobility support between the SGSN 115 and the SGW 108.
S12 is the reference point between UTRAN 120 and the SGW 108 for user plane tunneling when a direct tunnel is established.
The Home Subscriber Server (HSS) 123 is a subscriber database which comprises subscription-related information, performs authentication and authorization of the UE 101, and may provide information about the subscriber's location and Internet Protocol (IP) information. S6a is the reference point that enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system between the MME 105 and the HSS 123.
The Policy and Charging Rules Function (PCRF) 125 is a policy and charging control element. Gx is a reference point which provides transfer of policy and charging rules from the PCRF 125 to a Policy and Charging Enforcement Function (PCEF) in the PGW 110. The Rx reference point resides between the PCRF 125 and the Operator's IP Services 113.
The MME 105, the SGW 108, the PGW 110, the SGSN 115 and the HSS 123 may be seen as being part of a CN. The CN may be for example an Evolved Packet Core (EPC) of an LTE system.
A UE 101 needs to register with the network to receive services that require registration. This registration may be described as network attachment. When the UE 101 attaches to the EPC via the E-UTRAN 103, a PDN connection is created for the UE 101 during the attach procedure.
The NAS is a set of protocols in the Evolved Packet System (EPS). The NAS is used to convey non-radio signaling between the UE 101 and the MME 105 for an LTE/E-UTRAN access. The NAS procedures are grouped in two following two categories: the EPS Mobility Management (EMM) and the EPS Session Management (ESM).
The EMM protocol refers to procedures related to mobility over an E-UTRAN access, authentication and security. The ESM protocol offers support to the establishment and handling of user data in the NAS. PDN connection and EPS bearers are two concepts in ESM which defines the IP connectivity between the UE 101 and a PDN. EPS supports multiple simultaneous PDN connections. For instance, a UE 101 may have a PDN connection to the Internet (with a default EPS bearer) and one to the operator's IMS (with additional dedicated bearers, if required by the service).
If the UE 101 wishes to influence parameters (e.g. Access Point Name (APN), Protocol Configuration Options (PCO), etc.) of the PDN connection to be created during the attach procedure, the UE 101 requests the CN represented by the MME 105 to send an ESM Information Request message to the UE 101. When the UE 101 receives the ESM Information Request message, the UE 101 provides the parameters (e.g. APN, PCO, etc.) in an ESM Information Response message. An embodiment of such attach procedure is shown in FIGS. 2a and 2b, which is taken from chapter 5.3.2.1 in 3GPP TS 23.401 V12.4.0 (2014-03). FIG. 2a comprises steps 201-221 and FIG. 2b comprises steps 222-241, i.e. FIG. 2b is a continuation of FIG. 2a. The solid arrows in FIGS. 2a and 2b represent mandatory steps and the dotted arrows represent optional steps. The nodes involved in the procedure in FIGS. 2a and 2b are the UE 101, the eNodeB 103, the MME 105, the SGW 108, the PGW 110, the PCRF 125 and the HSS 123 as also seen in FIG. 1. In addition, an old MME/SGSN 130 and an Equipment Identity Register (EIR) 135 are also involved in the procedure in FIGS. 2a and 2b. In FIGS. 2a and 2b, the MME 105 is referred to as a new MME 105 because it is the MME to which the UE 101 attempts to attach. The old MME/SGSN 130 is the MME/SGSN which the UE 101 was previously attached, i.e. before start of the procedure in FIGS. 2a and 2b and before trying to attach to the new MME 105. The procedure in FIGS. 2a and 2b comprises the following steps, which steps may be performed in any suitable order than described below:
Step 201
This step is seen in FIG. 2a. The UE 101 initiates the attach procedure by the transmission of an Attach Request message to the eNodeB 103. The Attach Request message may comprise parameters such as e.g. International Mobile Subscriber Identity (IMSI) or old Globally Unique Temporary UE Identity (GUTI), Old GUTI type, last visited Tracking Area Identity (TAI) (if available), UE Core Network Capability, Radio Resource Control (RRC) parameters etc. The UE 101 may set a Ciphered Options Transfer Flag in the Attach Request message if it would like to send ESM information such as APN and PCO.
Step 202
This step is seen in FIG. 2a. The eNodeB 103 derives the new MME 105 e.g. from the RRC parameters. The eNodeB 103 forwards the Attach Request message to the new MME 105 for example comprised in an S1-MME control message.
Step 203
This step is seen in FIG. 2a. If the UE 101 identifies itself with GUTI and the MME has changed since detach, the new MME 105 determines the type of the old node, i.e. MME or SGSN 130. The new MME 105 may uses the GUTI received from the UE 101 to derive the old MME/SGSN 130 address, and sends an Identification Request message (comprising e.g. the old GUTI, complete Attach Request message) to the old MME/SGSN 130 to request the IMSI.
Step 204
This step is seen in FIG. 2a. The old MME/SGSN 130 responds with an Identification Response message comprising security parameters to the new MME 105, and the new MME 105 may store the received parameters for later use.
Step 205
This step is seen in FIG. 2a. If the UE 101 is unknown in both the old MME/SGSN 130 and the new MME 105, the new MME 105 sends an Identity Request message to the UE 101 to request the IMSI.
Step 206
This step is seen in FIG. 2a. The UE 101 sends an Identity Response message to the new MME 105 comprising the requested IMSI.
Step 207
This step is seen in FIG. 2a. If no UE context exists for the UE 101 anywhere in the network, if the Attach Request (sent in step 201) was not integrity protected, or if the check of the integrity failed, then an authentication and NAS security setup is performed.
Step 208
This step is seen in FIG. 2a. The new MME 105 sends an Identity Request message to the UE 101, and the UE 101 responds with an Identity Response message.
Step 209
This step is seen in FIG. 2a. The new MME 105 may send the Mobile Equipment (ME) Identity Check Request message to the EIR 130. The ME Identity Check Request comprises the ME Identity and the IMSI. The EIR 103 may respond with ME Identity Check Acknowledgement (i.e. the result of the identify check). Dependent upon the result, the new MME 105 decides whether to continue with this attach procedure or to reject the UE 101.
Steps 210 and 211
This step is seen in FIG. 2a. If the UE 101 has set the Ciphered Options Transfer Flag in the Attach Request message in step 201, the Ciphered Options i.e. PCO or APN or both, shall now be retrieved from the UE 101. This is done by the new MME 105 sending a Ciphered Options Request message to the UE 101. The UE 101 responds with a Ciphered Options Response message to the new MME 105 comprising the Ciphered Options, i.e. PCO or APN or both.
An APN is a reference to a gateway between e.g. the 4G mobile network and the Internet. The APN identifies the PDN that the UE 101 wants to communicate with. In addition to identifying a PDN, an APN may also be used to define the type of service, (e.g. connection to wireless application protocol (WAP) server, multimedia messaging service (MMS)) that is provided by the PDN. An APN may be translated to an IP address. The purpose of the PCO is to provide additional optional information about the destination network that the UE 101 is connecting to. For example, when a UE 101 connects to the Internet it will be given an IP address and it will be given a PCO that includes the default gateway IP address, the DNS server address, etc.
In order to handle situations where the UE 101 may have subscriptions to multiple PDNs, if the PCO comprises user credentials (e.g. user name/password within Password Authentication Protocol (PAP) or Challenge Handshake Authentication Protocol (CHAP) parameters) then the UE 101 should also send the APN to the new MME 105 in the Ciphered Options Response message.
The Ciphered Options Request message may also be referred to as an ESM Information Request message and the Ciphered Options Response message may be referred to as an ESM Information Response message. The term Ciphered Options Request/Response are terms used in 3GPP TS 23.401 and the terms ESM information request/response are terms used in 3GPP TS 24.301. Even though different terms are used, the Ciphered Options Request may be seen as being the same as the ESM information request message and the Ciphered Options Response message may be seen as being the same as the ESM Information Response message and the terms may be used interchangeably herein.
Step 212-214
This step is seen in FIG. 2a. If there are active bearer contexts in the new MME 105 for this particular UE 101 (i.e. the UE re-attaches to the same MME 105 without having properly detached before), the new MME 105 deletes these bearer contexts by sending Delete Session Request messages to the gateways involved, i.e. the SGW 108 and the PGW 110. The gateways 108, 110 acknowledge with Delete Session Response (Cause) message. If a PCRF 125 is deployed, the PGW 110 employs an Internet Protocol-Connectivity Access Network (IP-CAN) Session Termination procedure to indicate that resources have been released.
Step 215
This step is seen in FIG. 2a. The MME 105 sends an Update Location Request message to the HSS 123.
Step 216-217
This step is seen in FIG. 2a. The HSS 123 sends a Cancel Location message to the old MME 130. The old MME 130 acknowledges with a Cancel Location Acknowledgement message to the HSS 123.
Step 218-220
This step is seen in FIG. 2a. If there are active bearer contexts in the old MME/SGSN 130 for this particular UE 101, the old MME/SGSN 130 deletes these bearer contexts by sending Delete Session Request messages to the GWs involved, i.e. the SGW 108 and the PGW 110. The GWs 108, 110 return a Delete Session Response (Cause) message to the old MME/SGSN 130.
Step 221
This step is seen in FIG. 2a. The HSS 123 acknowledges the Update Location message by sending an Update Location Acknowledgement message to the new MME 105.
Step 222
This step is seen in FIG. 2b. The new MME 105 sends a Create Session Request message to the SGW 108.
Step 223
This step is seen in FIG. 2b. The SGW 108 creates a new entry in its EPS Bearer table and sends a Create Session Request message to the PGW 110 indicated by the PGW address received in the previous step 222.
Step 224
This step is seen in FIG. 2b. If dynamic Policy and Charging Control (PCC) is deployed and the Handover Indication is not present, the PGW 110 performs an IP-CAN Session Establishment procedure, i.e. a PCEF Initiated IP-CAN Session Establishment/Modification.
Step 225
This step is seen in FIG. 2b. The PGW 110 returns a Create Session Response message to the SGW 108.
Step 226
This step is seen in FIG. 2b. The PGW 110 sends a First Downlink Data (if not handover) to the SGW 108.
Step 227
This step is seen in FIG. 2b. The SGW 108 returns a Create Session Response message to the new MME 105.
Step 228
This step is seen in FIG. 2b. The new MME 105 sends an Initial Context Setup Request/Attach Accept message to the eNodeB 103. Such Attach Accept message comprises information about at least one supported EPS network feature, e.g. whether IMS voice over Packet Switched (PS) sessions is supported or not, and possibly also at least one Public Land Mobile Network (PLMN) which are equivalent to at least one registered PLMN. The registered PLMN is the PLMN in which the UE 101 is registered, e.g. the HPLMN. The eNodeB 103 forwards the Attach Accept message to the UE 101 (not illustrated in FIG. 2b). The Attach Accept message in step 228 is a response to the Attach Request message in step 201.
Step 229
This step is seen in FIG. 2b. The eNodeB 103 sends an RRC Connection Reconfiguration message to the UE 101.
Step 230
This step is seen in FIG. 2b. The UE 101 sends an RRC Connection Reconfiguration Complete message to the eNodeB 103.
Step 231
This step is seen in FIG. 2b. The eNodeB 103 sends an Initial Context Setup Response message to the new MME 105.
Step 232
This step is seen in FIG. 2b. The UE 101 sends a Direct Transfer message to the eNodeB 103.
Step 233
This step is seen in FIG. 2b. The eNodeB 103 sends an Attach Complete message to the new MME 105.
Step 234
This step is seen in FIG. 2b. After the Attach Accept message and once the UE 101 has obtained a PDN Address, the UE 101 may then send uplink packets, i.e. the first uplink data, towards the eNodeB 103 which will then be tunneled to the SGW 108 and the PGW 110.
Step 235
This step is seen in FIG. 2b. The new MME 105 sends a Modify Bearer Request message to the SGW 108.
Step 236
This step is seen in FIG. 2b. The SGW 108 sends a Modify Bearer Request message to the PGW 110.
Step 237
This step is seen in FIG. 2b. The PGW 110 sends a Modify Bearer Response message to the SGW 108.
Step 238
This step is seen in FIG. 2b. The SGW 108 sends a Modify Bearer Response message to the new MME 105.
Step 239
This step is seen in FIG. 2b. The SGW 108 sends its buffered downlink packets to the UE 101, i.e. the first downlink data.
Step 240
This step is seen in FIG. 2b. The new MME 105 sends a Notify Request message to the HSS 123.
Step 241
This step is seen in FIG. 2b. The HSS 123 sends a Notify Response message to the new MME 105.
As mentioned above, steps 210 and 211 seen in FIG. 2a are related to ESM information.
So, the UE 101 provides the ESM information (e.g. APN, PCO or both) of a first PDN connection over E-UTRAN in the ESM Information Response message/Ciphered Options Response message in step 211. After the UE 101 has provided the ESM information of the first PDN connection over E-UTRAN, the new MME 105 sends an Attach Accept message to the eNodeB 103 in step 228. With the Attach Accept message information such as e.g. information about at least one supported EPS network feature (e.g. whether IMS voice over PS sessions is supported or not), at least one PLMN which is equivalent to the registered PLMN etc. is comprised.
There are situations when the UE 101 would like to indicate parameters such as e.g. APN, PCO, depending on whether the UE 101 roams or is at home. In one example, the UE 101 wants to have the PDN connection with Internet APN when at home. Another example is that the UE 101 does not want the PDN connection with Internet APN when roaming (e.g. does not want to be charged the roaming fees of the Internet access) and instead the UE 101 will create a PDN connection to IMS APN. The term home refers to the Home PLMN (HPLMN) of the UE 101 and is the network in which the subscriber's profile of the UE 101 is held. When a UE 101 is roaming it may be in a Visited PLMN (VPLMN), i.e. when the UE 101 loses coverage of its HPLMN. When the UE 101 is roaming it may receive services from a PLMN which is different from its HPLMN. A HPLMN and VPLMN may be operated by different network operators or by the same network operator.
When the UE 101 attaches to a PLMN other than the HPLMN of the UE 101, i.e. it attaches to a VPLMN, and when the equivalent PLMNs Information Element (IE) indicated in an Attach Accept message (see step 228 in FIG. 2) comprises the HPLMN of the UE 101 the UE 101 may believe it is roaming until the Attach Accept message is received. The UE 101 may believe it is at home (since 3GPP TS 22.011 states: “It shall also be possible to indicate to the UE 101 that a group of PLMNs are equivalent to the registered PLMN regarding PLMN selection, cell selection/re-selection and handover.”) after the Attach Accept message is received by the UE 101. However, an ESM Information Response message needs to be sent before an Attach Accept message is received. The equivalent PLMN may be abbreviated EPLMN or EHPLMN (Equivalent HPLMN). The EPLMN or EHPLMN defines a set of PLMN which are treated as equivalent to PLMN with which UE 101 is registering.
Thus, when the UE 101 attaches to a PLMN other than the HPLMN of the UE 101, when sending the ESM Information Response message, the UE 101 does not know whether it is going to be roaming (if the equivalent PLMN information is indicated in a later received Attach Accept message is not comprised or does not comprise the HPLMN of the UE 101), or whether it is going to be at home (if the equivalent PLMN information indicated in the later received Attach Accept comprises the HPLMN of the UE 101) and parameters of the PDN connection to be created may be setup incorrectly.